Shaping of pulses in optical grating-based laser systems for optimal control of electrons in laser plasma wake-field accelerator

In typical chirped pulse amplification (CPA) laser systems, scanning the grating separation in the optical compressor causes the well known generation of linear chirp of frequency vs. time in a laser pulse, as well as a modification of all the higher order phase terms. By setting the compressor angle slightly different from the optimum value to generate the shortest pulse, a typical scan around this value will produce significant changes to the pulse shape. Such pulse shape changes can lead to significant differences in the interaction with plasmas such as used in laser wake-field accelerators. Strong electron yield dependence on laser pulse shape in laser plasma wake-field electron acceleration experiments have been observed in the L´OASIS Lab of LBNL [W.P. Leemans, P. Catravas, E. Esarey, C.G.R. Geddes, C. Toth, R. Trines, C.B. Schroeder, B.A. Shadwick, J. van Tilborg, and J. Faure, Phys. Rev. Lett. 89, 174802 (2002)]. These experiments show the importance of pulse skewness parameter, S, defined here on the basis of the ratio of the ´head-width-half-max´ (HWHM) and the ´tail-width-half-max´ (TWHM), respectively.